Methods and devices for drug delivery to ocular tissue using microneedle

ABSTRACT

Methods and devices are provided for targeted administration of a drug to a patient&#39;s eye. In one embodiment, the method includes inserting a hollow microneedle into the sclera of the eye at an insertion site and infusing a fluid drug formulation through the inserted microneedle and into the suprachoroidal space of the eye, wherein the infused fluid drug formulation flows within the suprachoroidal space away from the insertion site during the infusion. The fluid drug formulation may flow circumferentially toward the retinochoroidal tissue, macula, and optic nerve in the posterior segment of the eye.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/767,768, filed Apr. 26, 2010, now pending, which is acontinuation-in-part of U.S. application Ser. No. 11/743,535, filed May2, 2007, now U.S. Pat. No. 7,918,814, issued Apr. 5, 2011, which claimsbenefit of U.S. Provisional Application No. 60/746,237, filed May 2,2006. Benefit is also claimed to U.S. Provisional Application No.61/172,409, filed Apr. 24, 2009. These applications are incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with U.S. government support under Contract No.8 ROI EB00260-03 and Contract No. R24EY017045-01, which were awarded bythe National Institute of Health. The U.S. government has certain rightsin the invention.

BACKGROUND OF THE INVENTION

This invention is generally in the field of ophthalmic therapies, andmore particularly to the use of a microneedle for infusion of a fluiddrug formulation into ocular tissues for targeted, local drug delivery.

The delivery of drug to the eye is extremely difficult, particularlydelivery of macromolecules and delivery to the back of the eye. Manyinflammatory and proliferative diseases in the posterior region of theeye require long term pharmacological treatment. Examples of suchdiseases include macular degeneration, diabetic retinopathy, anduveitis. It is difficult to deliver effective doses of drug to the backof the eye using conventional delivery methods such as topicalapplication, which has poor efficacy, and systemic administration, whichoften causes significant side effects. (Geroski & Edelhauser, Invest.Ophthalmol. Vis. Sci. 41:961-64 (2000)). For example, while eye dropsare useful in treating conditions affecting the exterior surface of theeye or tissues at the front of the eye, the eye drops cannotsignificantly penetrate to the back of the eye, as may be required forthe treatment of various retinal diseases.

Direct injection into the eye, using conventional needles and syringesis often effective, but requires professional training and raisesconcerns about safety (Maurice, J. Ocul. Pharmacol. Ther. 17:393-401(2001)). It also would be desirable to be able to minimize the numberand/or frequency of eye injection treatments needed to delivertherapeutically effective amounts of drug to the ocular tissue sitesthat need it.

The suprachoroidal space of the eye has been studied, and itscannulation described as a possible route for drug delivery. See, e.g.,Olsen, et al., American J. Ophthalmology 142(5): 777-87 (November 2006);PCT Patent Application Publication No. WO 2007/100745 to IscienceInterventional Corporation.

It therefore would be desirable to provide better, safer, more effectivetechniques for the direct delivery of therapeutic agents to eye tissues.It also would be desirable to provide devices useful in such techniqueswhich can be relatively inexpensive to produce and use. It further wouldbe desirable to provide methods for pinpoint delivery of drug to sclera,choroidal, uveal, macular, ciliary, vitreous and retinal tissues.

SUMMARY OF THE INVENTION

Methods and devices are provided for administering a drug to an eye of apatient. The methods may be used, for example, in the treatment ofuveitis, glaucoma, diabetic macular edema, age-related maculardegeneration, or cytomegalovirus retinitis. In one aspect, the methodincludes inserting a hollow microneedle into the sclera of the eye at aninsertion site, the microneedle having a tip end with an opening; andinfusing over a period of time a fluid drug formulation, which comprisesa drug, through the inserted microneedle and into the suprachoroidalspace of the eye, wherein during the period the infused drug formulationflows within the suprachoroidal space away from the insertion site.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, and 1D are cross-sectional illustrations of the tissuestructures of a human eye. The eye as a whole (1A), a close-up of thecornea (1B), and a close-up of the sclera and associated tissues in aneye without fluid in the suprachoroidal space (1C) or with fluid in thesuprachoroidal space (1D).

FIG. 2 is a cross-sectional view of a microneedle device comprising ahollow microneedle disposed in an elongated body according to oneembodiment.

FIG. 3 is a cross-sectional view of the elongated body of themicroneedle devices shown in FIG. 2.

FIG. 4 is an illustration of a microneedle device according to oneembodiment.

FIG. 5 is an illustration of a microneedle device according to oneembodiment.

FIGS. 6A and 6B illustrate an embodiment of a process for using a hollowmicroneedle to deliver drug into the suprachoroidal space of an eye,where the process includes inserting the hollow microneedle into thesclera and infusion of a fluid drug formulation into the suprachoroidalspace.

FIG. 7A shows a comparison of a hollow microneedle according to oneembodiment as compared to the tip of a conventional 30 gauge hypodermicneedle. FIG. 7B shows a schematic illustration of a custom acrylic moldshaped to fit a whole eye.

FIGS. 8A and 8B are brightfield microscopic images of saggital crosssections of a pig eye before and after infusion of sulforhadamine,respectively.

FIGS. 9A, 9B, 9C, and 9D are fluoroscopic images of a cryosection of apig eye with no infusion into the suprachoroidal space (9A), acryosection of a rabbit eye after infusion of 500 nm fluorescentparticles in the axial plan and collaged to form a panoramic view (9B),a cryosection of a pig eye after infusion of 500 nm fluorescentparticles in the saggital direction and collaged to show the spaces bothanterior and posterior to the microneedle insertion site (9C), and acryosection of a human eye after infusion of 500 nm fluorescentparticles in the saggital direction and collaged to show spaces bothanterior and posterior to the microneedle insertion site (9D). Theinsets of FIGS. 9B, 9C, and 9D show magnified views of the microneedleinsertion site.

FIGS. 10A and 10B are microcomputed tomography images showing thecircumferential spread of 1 μm contrast particles infused into thesuprachoroidal space of a pig eye in a cross-sectional image (10A) and athree-dimensional reconstruction of the cross-sectional images (10B).

FIGS. 11A, 11B, 11C, and 11D are graphs showing the effect of infusionpressure and microneedle length on the success rate of suprachoroidaldelivery of 20 nm particles (11A), 100 nm particles (11B), 500 nmparticles (11C), and 1000 nm particles (11D) into pig eyes.

FIGS. 12A and 12B are fluoroscopic images of a cryosection of a pig eyeafter infusion of 20 nm particles (12A) and 1000 nm particles (12B) inthe saggital direction and collaged to show spaces both anterior andposterior to the microneedle insertion site. The insets of FIGS. 12A and12B show magnified views of the microneedle insertion site.

FIGS. 13A and 13B are graphs showing the effect of the intraocularpressure and microneedle length on the success rate of suprachoroidaldelivery of 1000 nm particles for a simulated intraocular pressure of 18mmHg (13A) and 36 mmHg (13B).

FIG. 14 is a one-dimensional line of sight scan of rabbit eyes takenafter injection of sodium fluorescein to the suprachoroidal space, withthe x-axis representing the position in the eye from back (0) to front(160) and the y-axis representing the fluorescent intensity at thatposition.

FIG. 15 is a graph showing the rate of clearance of sodium fluoresceinfrom the suprachoroidal space over time.

FIG. 16 is a graph showing the rate of clearance of 20 nm particles fromthe suprachoroidal space over time.

FIG. 17 is a graph showing the rate of clearance of 500 nm particlesfrom the suprachoroidal space over time.

FIG. 18 is a block diagram of a method for administering a drug to theeye according to one embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An effective drug delivery system for delivery of a drug to the eyeshould optimally embody four general characteristics: first, it shouldbe minimally invasive and safe; second, the drug should be administeredin such a way that it is well targeted to the desired tissues and limitsexposure to other regions of the eye; third, it should be capable ofcontrolled or sustained delivery of the drug; and fourth, it should beas simple to use as possible. Embodiments of the present descriptionaddress these needs by providing microneedle devices and methods of useto enhance the delivery of a drug to the eye.

In one advantageous and exemplary embodiment of the methods describedherein, delivery of a drug is achieved by injecting (inserting) amicroneedle into the sclera and injecting (infusing) a drug formulationthrough the inserted microneedle and into the suprachoroidal space ofthe eye. The microneedle is able to precisely deliver the drug into thesuprachoroidal space for subsequent local delivery to nearby tissues inneed of treatment. The drug may be released into the ocular tissues fromthe infused volume (or, e.g., from the microparticles therein) for anextended period, e.g., several hours or days or weeks or months, afterthe microneedle has been inserted and withdrawn. This beneficially canprovide increased bioavailability of the drug relative, for example, todelivery by topical application of the drug formulation to ocular tissuesurfaces. With the present microneedle, the method advantageouslyincludes precise control of the depth of insertion into the oculartissue, so that the microneedle tip can be placed into thesuprachoroidal space or in the sclera but near enough to thesuprachoroidal space for the infused drug formulation to flow into thesuprachoroidal space. Advantageously, this may be accomplished withoutcontacting underlying tissues, such as choroid and retina tissues.

Microneedles enable this delivery to be done in a minimally invasivemanner superior to conventional needle approaches. For instance, thepresent microneedles advantageously may be inserted perpendicularly intothe sclera, reaching the suprachoroidal space in a short penetrationdistance. This is in contrast to long conventional needles or cannulawhich must approach the suprachoroidal space at a steep angle, taking alonger penetration path through the sclera and other ocular tissue,increasing the size of the needle track and consequently increasing therisk of infection and/or vascular rupture. With such long needles, theability to precisely control insertion depth is diminished relative tothe microneedle approach described herein.

Advantageously, the delivery of the drug into the suprachoroidal spaceallows for the delivery of fluid drug formulation over a larger tissuearea and to more difficult to target tissues in a single administrationas compared to previously known needle devices. Not wishing to be boundby any theory, it is believed that upon entering the suprachoroidalspace the fluid drug formulation flows circumferentially from theinsertion site toward the retinochoroidal tissue, macula, and opticnerve in the posterior segment of the eye as well as anteriorly towardthe uvea and ciliary body. In addition, a portion of the infused fluiddrug formulation may remain in the sclera near the microneedle insertionsite, serving as additional depot of the drug formulation thatsubsequently can diffuse into the suprachoroidal space and then intoother adjacent tissues.

As used herein, the term “suprachoroidal space,” which is synonymouswith suprachoroid or suprachoroidia, describes the potential space inthe region of the eye disposed between the sclera and choroid. Thisregion primarily is composed of closely packed layers of long pigmentedprocesses derived from each of the two adjacent tissues; however, aspace can develop in this region as a result of fluid or other materialbuildup in the suprachoroidal space and the adjacent tissues. Thoseskilled in the art will appreciate that the suprachoroidal spacefrequently is expanded by fluid buildup because of some disease state inthe eye or as a result of some trauma or surgical intervention. In thepresent description, however, the fluid buildup is intentionally createdby infusion of a drug formulation into the suprachoroid to create thesuprachoroidal space (which is filled with drug formulation). Notwishing to be bound by any theory, it is believed that this regionserves as a pathway for uveoscleral outflow (i.e., a natural process ofthe eye moving fluid from one region of the eye to the other through)and becomes a real space in instances of choroidal detachment from thesclera.

Methods of Using the Microneedle

The microneedle devices described herein may be used to deliver drugformulations to the eye of a patient, particularly for the treatment,diagnosis, or prevention of ocular diseases. In a preferred embodiment,the patient is a human patient in need of treatment. The patient may bean adult or a child. In other embodiments, the patient may be anon-human mammal.

A wide range of ocular diseases and disorders may be treated by themethods and devices described herein. Non-limiting examples of oculardiseases include uveitis, glaucoma, diabetic macular edema orretinopathy, macular degeneration, and genetic diseases. The methodsdescribed herein are particularly useful for the local delivery of drugsthat need to be administered to the posterior region of the eye, forexample the retinochoroidal tissue, macula, and optic nerve in theposterior segment of the eye. In one embodiment, the delivery methodsand devices described herein may be used in gene-based therapyapplications. For example, the methods may administer a fluid drugformulation into the suprachoroidal space to deliver select DNA, RNA, oroligonucleotides to targeted ocular tissues.

The microneedles can be used to target delivery to specific tissues orregions within the eye or in neighboring tissue. In various embodiments,the methods may be designed for drug delivery specifically to thesclera, the choroid, the Bruch's membrane, the retinal pigmentepithelium, the subretinal space, the retina, the macula, the opticdisk, the optic nerve, the ciliary body, the trabecular meshwork, theaqueous humor, the vitreous humor, and other ocular tissue orneighboring tissue in need of treatment.

As used herein, “ocular tissue” and “eye” 10 include both the anteriorsegment 12 of the eye (i.e., the portion of the eye in front of thelens) and the posterior segment 14 of the eye (i.e., the portion of theeye behind the lens), as illustrated in FIG. 1A. The anterior segment 12is bounded by the cornea 16 and the lens 18, while the posterior segment14 is bounded by the sclera 20 and the lens 18. The anterior segment 12is further subdivided into the anterior chamber 22, between the iris 24and the cornea 16, and the posterior chamber 26, between the lens 18 andthe iris 24. The exposed portion of the sclera 20 on the anteriorsegment 12 of the eye is protected by a clear membrane referred to asthe conjunctiva (not shown). Underlying the sclera 20 is the choroid 28and the retina 27, collectively referred to as retinachoroidal tissue.The loose connective tissue, or potential space, between the choroid 28and the sclera 20 is referred to as the suprachoroidal space (notshown). FIG. 1B illustrates the cornea 16, which is composed of theepithelium 30, the Bowman's layer 32, the stroma 34, the Descemet'smembrane 36, and the endothelium 38. FIG. 1C and FIG. 1D illustrate thesclera 20 with surrounding Tenon's Capsule 40 or conjunctiva 41,suprachoroidal space 42, choroid 28, and retina 27, both without andwith a fluid in the suprachoroidal space, respectively.

The method of administering a drug to the eye generally comprises thesteps of inserting a hollow microneedle into the sclera and theninfusing a fluid drug formulation through the hollow microneedle andinto the suprachoroidal space of the eye.

Insertion

In one embodiment, the insertion site is between the equator and thelimbus of the eye. In another embodiment, the insertion site is betweenabout 2 mm and about 10 mm posterior to the limbus of the eye. Inembodiments, the insertion site of the microneedle is at about theequator of the eye. In another embodiment, the insertion site is betweenthe equator and the limbus of the eye. In another embodiment, theinsertion site is from 2 to 10 mm posterior to the limbus of the eye. Inanother embodiment, the drug formulation is introduced into thesuprachoroidal space at the site of injection (i.e., at the tip of themicroneedle) and then flows through the suprachoroidal space away fromthe site of injection while the injection occurs. In another embodiment,the site of injection (i.e., at the tip of the microneedle) is anteriorto the equator of the eye and at least a portion of the drug formulationflows posterior to the equator of the eye during the injection (i.e.,while drug formulation continues to flow out of the microneedle). Inanother embodiment, the site of injection (i.e., at the tip of themicroneedle) is anterior to the equator of the eye and at least aportion of the drug formulation flows near the macular during theinjection (i.e., while drug formulation continues to flow out of themicroneedle).

Importantly, the depth of insertion of the microneedle into the oculartissue is precisely controlled. Various methods can be used to controlthe insertion depth of the microneedles described herein. In aparticular embodiment, the insertion depth is limited by the selectedlength or effective length of the microneedle. The “effective length” isthat portion available for tissue insertion, i.e., the length thatextends from the base and would be inserted if there were zero tissuedeformation; it neglects any proximal portion of the microneedle thatextends into or through the base and thus cannot be inserted in thetissue. That is, the microneedle may have a length approximately equalto the desired penetration depth. In one embodiment, the microneedle isshort enough that tip of the microneedle may be inserted substantiallyto the base of the sclera (i.e., near the interface of the sclera andchoroid) without completely penetrating across the sclera. In anotherembodiment, the tip of the microneedle is inserted through the sclerainto the suprachoroidal space without penetrating through the choroid.

In another embodiment, the microneedles are designed to have a lengthlonger than the desired penetration depth, but the microneedles arecontrollably inserted only part way into the tissue. Partial insertionmay be controlled by the mechanical properties of the tissue, whichbends and dimples during the microneedle insertion process. In this way,as a microneedle is inserted into the tissue, its movement partiallyelastically deforms the tissue and partially penetrates into the tissue.By controlling the degree to which the tissue deforms, the depth ofmicroneedle insertion into the tissue can be controlled.

Additional insertion control features are described below in the“Control Features for Directing Movement of the Microneedle in theMethods of Use” section below.

In another embodiment, a microneedle is inserted into the tissue using arotational/drilling technique and/or a vibrating action. In this way,the microneedle can be inserted to a desired depth by, for example,drilling the microneedles a desired number of rotations, whichcorresponds to a desired depth into the tissue. See, e.g., U.S. PatentApplication Publication No. 20050137525 A1 to Wang et al., which isincorporated herein by reference, for a description of drillingmicroneedles. The rotational/drilling technique and/or a vibratingaction may be applied during the insertion step, retraction step, orboth.

Infusion

In a preferred embodiment, the fluid drug formulation is infused intothe suprachoroidal space through a hollow microneedle by driving thedrug formulation from a source reservoir into the ocular tissue using apressure gradient (e.g., pumping, syringe). In other embodiments, thedrug formulation may be driven from a source reservoir into the oculartissue using an electric field (e.g., iontophoresis) or anotherexternally applied energy (e.g., ultrasound/acoustic energy).

In one embodiment, the amount of fluid drug formulation infused into thesuprachoroidal space from the inserted microneedle is from 10 microliterto 200 microliter, e.g., from 50 to 150 μL. In another embodiment, fromabout 10 microliter to about 500 microliter, e.g., from 50 to 250 μL, isinfused through the microneedle into the suprachoroidal space.

In one embodiment, the driving force or pressure infusing the fluid drugformulation through the microneedle causes the infused drug formulationto flow within the suprachoroidal space and reach the back of the eyeduring the administration (i.e., during the infusion) process. This mayoccur in less than one or two minutes, such as 1 sec to 100 sec, e.g.,10 to 30 seconds. In one aspect, the fluid drug formulation desirablyflows circumferentially within the suprachoroidal space during theinfusion process to a site that is at least 2.5 mm away from theinsertion site, to a site that is at least 5 mm away from the insertionsite, or to a site that is at least 10 mm away from the insertion site.Desirably, the fluid drug formulation flows circumferentially within thesuprachoroidal space from the insertion site toward the back of the eye(i.e., the retinochoroidal tissue, macula, and optic nerve in theposterior segment of the eye).

The amount of drug delivered within the ocular tissue also may becontrolled, in part, by the type of microneedle used and how it is used.In one exemplary embodiment, a hollow microneedle is inserted into theocular tissue and progressively retracted from the ocular tissue afterinsertion to deliver a fluid drug, where after achieving a certaindosage, the delivery could be stopped by deactivating the fluid drivingforce, such as pressure (e.g., from a mechanical device such as asyringe) or an electric field, to avoid leakage/uncontrolled deliver ofdrug. Desirably, the amount of drug being delivered is controlled bydriving the fluid drug formulation at a suitable infusion pressure. Incertain embodiments, the infusion pressure may be at least 150 kPa, atleast 250 kPa, or at least 300 kPa. Suitable infusion pressures may varywith the particular patient or species.

Those skilled in the art will appreciate, however, that the desiredinfusion pressure to deliver a suitable amount of fluid drug formulationmay be influenced by the depth of insertion of the microneedle and thecomposition of the fluid drug formulation. For example, a greaterinfusion pressure may be required in embodiments wherein the drugformulation for delivery into the eye is in the form of or includesnanoparticles or microparticles encapsulating the active agent ormicrobubbles. Nanoparticle or microparticle encapsulation techniques arewell known in the art.

Additional infusion control features are described below in the “Controlof Transport Through Microneedle” section below.

In one embodiment, the method of administering a drug to the eye mayfurther include partially retracting the hollow microneedle after theinsertion step and before and/or during the infusion of the drugformulation. In a particular embodiment, the partial retraction of themicroneedle occurs prior to the step of infusing the fluid drugformulation into the ocular tissue. This insertion/retraction step mayform a pocket and beneficially permits the fluid drug formulation toflow out of the microneedle unimpeded or less impeded by ocular tissueat the opening at the tip portion of the microneedle. This pocket may befilled with drug formulation, but also serves as a conduit through withfluid drug formulation can flow from the microneedle, through the pocketand into the suprachoroidal space. FIG. 6A shows a hollow microneedle130 inserted into the sclera 20, with drug formulation 131 temporarilypositioned in the hollow bore of the microneedle. (The fluidcommunication to a reservoir of the fluid drug formulation is notshown.) FIG. 6B shows the microneedle 130 following partial retractionand infusion of the fluid drug formulation 131 into the suprachoroidalspace. Arrows show the circumferential flow of the drug formulationthrough the suprachoroidal space.

In a particular embodiment, the microneedle infuses a drug formulationthrough the sclera into the suprachoroidal space for controlled (i.e.,sustained, extended, or modulated over time) release of a drug to one ormore ocular or neighboring tissues. This “sustained release” or“extended release” or “modulated release” is generally more prolongedthan that obtainable by topical application of the drug formulation tothe ocular tissue. In a particular embodiment, there is an extended,sustained or modulated release of the drug formulation after at leastone microneedle is withdrawn from the ocular tissue. This deliverymethod can be particularly advantageous with ocular tissues, where it isdesirable for the insertion and withdrawal process to occur over asshort a period as possible to minimize patient discomfort—in contrast totransdermal microneedle patch applications, where patches may morelikely be worn (with microneedles inserted) over an extended periodwithout patient discomfort.

Other Steps, Embodiments, and Applications

In another aspect, the method of administering a drug to an eye of apatient may include monitoring the insertion of the microneedle and/orinfusion of the fluid drug formulation to ensure precise delivery of thefluid drug formulation to the suprachoroidal space (FIG. 18). Suchmonitoring may be achieved using imaged-guided feedback methods duringone or more of these steps, non-limiting examples of which includeconventional microscopy, MRI, x-ray, confocal microscopy, ocularcoherence tomography (e.g., anterior segment optical coherencetomography, Heidelberg retina tomography, spectral domain opticalcoherence tomography), fluorescein angiography, indocyanine greenangiography, high resolution stereoscopic fundus photography,autofluorescence imaging, ultra-wide field imaging, and variousultrasound techniques. Thus, the method may further comprise determiningwhether an initial infusion of the fluid drug formulation has flowedinto the suprachoroidal space of the eye and away from the insertionsite. If it is determined that an initial infusion has been successful,a desired volume of the fluid drug formulation can be infused and theinfusion discontinued by removing the fluid driving force, such aspressure, and retracting the microneedle from the eye. If, however, itis determined that the initial infusion of the fluid drug formulationhas been unsuccessful (i.e., substantially none of the drug formulationhas flowed into the suprachoroidal space of the eye and away from theinsertion site), then the microneedle may be repositioned and theprocess repeated until a successful delivery is achieved.

The microneedle optionally may be part of an array of two or moremicroneedles such that the method further includes inserting at least asecond microneedle into the sclera without penetrating across thesclera. In one embodiment wherein an array of two or more microneedlesare inserted into the ocular tissue, the drug formulation of each of thetwo or more microneedles may be identical to or different from oneanother, in drug formulation, volume/quantity of drug formulation, or acombination of these parameters. In one case, different types of drugformulations may be injected via the one or more microneedles. Forexample, inserting a second hollow microneedle comprising a second drugformulation into the ocular tissue will result in delivery of the seconddrug formulation into the ocular tissue.

The microneedle devices described herein may be adapted to removesubstances, such as a fluid, tissue, or molecule sample, from the eye.

Those skilled in the art will appreciate, however, that other types ofmicroneedles solid microneedles) and other methods of delivering thedrug formulation into the ocular tissue, may be used instead of or inconjunction with the infusion methods described herein. Non limitingexamples include dissolving, at least in part, a coating of a drugformulation off of a microneedle; detaching, at least in part, a coatingof a drug formulation (e.g., as a substantially intact sleeve or infragments) off of a microneedle; breaking or dissolving a microneedleoff of a base to which the microneedle is integrally formed or isconnected; or any combination thereof.

The microneedle devices described herein also may be adapted to use theone or more microneedles as a sensor to detect analytes, electricalactivity, and optical or other signals. The sensor may include sensorsof pressure, temperature, chemicals, and/or electromagnetic fields(e.g., light). Biosensors can be located on or within the microneedle,or inside a device in communication with the body tissue via themicroneedle. The microneedle biosensor can be any of the four classes ofprincipal transducers: potentiometric, amperometric, optical, andphysiochemical. In one embodiment, a hollow microneedle is filled with asubstance, such as a gel, that has a sensing functionality associatedwith it. In an application for sensing based on binding to a substrateor reaction mediated by an enzyme, the substrate or enzyme can beimmobilized in the needle interior. In another embodiment, a wave guidecan be incorporated into the microneedle device to direct light to aspecific location, or for detection, for example, using means such as apH dye for color evaluation. Similarly, heat, electricity, light,ultrasound or other energy forms may be precisely transmitted todirectly stimulate, damage, or heal a specific tissue or for diagnosticpurposes.

The Microneedle Device

The microneedle device includes a hollow microneedle. The device mayinclude an elongated housing for holding the proximal end of themicroneedle. The device may further include a means for conducting afluid drug formulation through the microneedle. For example, the meansmay be a flexible or rigid conduit in fluid connection with the base orproximal end of the microneedle. The means may also include a pump orother devices for creating a pressure gradient for inducing fluid flowthrough the device. The conduit may in operable connection with a sourceof the fluid drug formulation. The source may be any suitable container.In one embodiment, the source may be in the form of a conventionalsyringe. The source may be a disposable unit dose container.

Microneedle

As used herein, the term “hollow” includes a single, straight borethrough the center of the microneedle, as well as multiple bores, boresthat follow complex paths through the microneedles, multiple entry andexit points from the bore(s), and intersecting or networks of bores.That is, a hollow microneedle has a structure that includes one or morecontinuous pathways from the base of the microneedle to an exit point inthe shaft and/or tip portion of the microneedle distal to the base.

As used herein, the term “microneedle” refers to a conduit body having abase, a shaft, and a tip end suitable for insertion into the sclera andother ocular tissue and has dimensions suitable for minimally invasiveinsertion and fluid drug formulation infusion as described herein. Thatis, the microneedle has a length or effective length that does notexceed 2000 microns and a width (or diameter) that does not exceed 500microns.

In various embodiments, the microneedle may have a length of about 50 μmto 2000 μm. In another particular embodiment, the microneedle may have alength of about 150 μm to about 1500 μm, about 300 μm to about 1250 μm,about 500 μm to about 1250 μm, about 700 μm to about 1000 μm, or about800 to about 1000 μm. In a preferred embodiment, the length of themicroneedle is about 1000 μm. In various embodiments, the proximalportion of the microneedle has a maximum width or cross-sectionaldimension of about 50 μm to 500 μm, about 50 μm to about 400 μm, about100 μm to about 400 μm, about 200 μm to about 400 μm, or about 100 μm toabout 250 μm, with an aperture diameter of about 5 μm to about 400 μm.In a particular embodiment, the proximal portion of the microneedle hasa maximum width or cross-sectional dimension of about 400 μm. Thoseskilled in the art will appreciate, however, that in embodiments inwhich the tip of the microneedle is beveled that the aperture diametermay be greater than the outer diameter of the proximal portion of themicroneedle. The microneedle may be fabricated to have an aspect ratio(width:length) of about 1:1.5 to about 1:10. Other lengths, widths, andaspect ratios are envisioned.

The microneedle can have a straight or tapered shaft. In one embodiment,the diameter of the microneedle is greatest at the base end of themicroneedle and tapers to a point at the end distal the base. Themicroneedle can also be fabricated to have a shaft that includes both astraight (i.e., untapered) portion and a tapered (e.g., beveled)portion. The microneedles can be formed with shafts that have a circularcross-section in the perpendicular, or the cross-section can benon-circular. The tip portion of the microneedles can have a variety ofconfigurations. The tip of the microneedle can be symmetrical orasymmetrical about the longitudinal axis of the shaft. The tips may bebeveled, tapered, squared-off, or rounded. In particular embodiments,the microneedle may be designed such that the tip portion of themicroneedle is substantially the only portion of the microneedleinserted into the ocular tissue (i.e., the tip portion is greater than75% of the total length of the microneedle, greater than 85% of thetotal length of the microneedle, or greater than about 95% of the totallength of the microneedle). In other particular embodiments, themicroneedle may be designed such that the tip portion is only a portionof the microneedle that is inserted into the ocular tissue and generallyhas a length that is less than about 75% of the total length of themicroneedle, less than about 50% of the total length of the microneedle,or less than about 25% of the total length of the microneedle. Forexample, in one embodiment the microneedle has a total effective lengthbetween 500 μm and 1000 μm, wherein the tip portion has a length that isless than about 400 μm, less than about 300 μm, or less than about 200μm.

Base

The microneedle extends from a base. The base may be integral with orseparate from the microneedle. The base may be rigid or flexible. Thebase may be substantially planar or it may be curved, for example, inthe shape of the ocular tissue surface at the site of injection or, forexample, curved away from the ocular surface (e.g., convex) so as tominimize contact between the base and the ocular tissue. Desirably, thebase is shaped to provide minimal contact with the surface of the eye atthe point of insertion. For example, in one embodiment, the base mayextend only a minimal distance from the microneedle shaft substantiallyperpendicular. In another embodiment, the base may be shaped so as toelevate the ocular tissue towards the microneedle so as to counteractthe deflection of the ocular tissue and facilitate insertion of themicroneedle into the ocular tissue (e.g., the base may extend from themicroneedle toward the tip portion of the microneedle so as to “pinch”the ocular tissue). Some such embodiments may be based, at least inpart, on the devices described in U.S. Pat. No. 6,743,211, the relevantdisclosure of which is incorporated herein by reference.

In a particular embodiment, the microneedle device has a singlemicroneedle. In one embodiment, illustrated in FIG. 5, the microneedledevice 130 includes a convex base 132 and a hollow microneedle 134 whichhas a bore 140 through which a fluid drug formulation (not shown) can bedelivered to the eye or through which a biological fluid can bewithdrawn from the eye. The hollow microneedle 134 includes a proximalportion 136 and a tip portion 138.

The microneedle may extend from the base of the microneedle device atany angle suitable for insertion into the eye. In a particularembodiment, the microneedle extends from the base at an angle of about90 degrees to provide approximately perpendicular insertion of themicroneedles into the surface of the eye. In another particularembodiment, the microneedle extends from the base at an angle from about60 to about 90 degrees.

Microneedle Arrays

In an alternative embodiment, the device includes an array of two ormore microneedles. For example, the device may include an array ofbetween 2 and 1000 (e.g., between 2 and 100) microneedles. In oneembodiment, a device may include between 1 and 10 microneedles. An arrayof microneedles may include a mixture of different microneedles. Forinstance, an array may include microneedles having various lengths, baseportion diameters, tip portion shapes, spacings between microneedles,drug coatings, etc. In embodiments wherein the microneedle devicecomprises an array of two or more microneedles, the angle at which asingle microneedle extends from the base may be independent from theangle at which another microneedle in the array extends from the base.

Exemplary Devices

FIGS. 2-5 illustrate exemplary embodiments of microneedle devices. Inone embodiment, illustrated in FIG. 2-3, the microneedle device 110includes a hollow microneedle 114 having a hollow bore 140 through whicha fluid drug formulation (not shown) can be delivered to the eye orthrough which a biological fluid can be withdrawn from the eye. Themicroneedle includes a proximal portion 116 and a tip portion 118. Themicroneedle 114 may extend from a base comprising, for example, anelongated body 112 having a distal end from which the proximal portion116 and tip portion 118 of the microneedle extends. The elongated bodymay further comprise a means for securing 111 a base portion of themicroneedle extending beyond the distal end of the base 112, such as ascrew or pin. An exemplary embodiment of the elongated body 112 forsecuring the microneedle is illustrated in FIG. 3, and comprises a capportion 113 and a base portion 115 having a hollow bore 117 therein. Thecap portion 113 and base portion 115 of the elongated body 112 desirablycomprise a means for manually adjusting the length of needle (i.e., theproximal portion and tip portion of the microneedle extending from thebase 112) protruding out of the cap portion of the elongated body. Suchmeans may include, for example, threads 119 allowing the cap portion 113to be screwed in and out of the base portion 115 of the elongated body.In an exemplary embodiment illustrated in FIG. 4, the base portion 115of the elongated body may be operably connected to an actuator 120 forcontrolled infusion of the fluid drug formulation through themicroneedle into the suprachoroidal space.

The microneedle device may further comprise a fluid reservoir forcontaining the fluid drug formulation, the fluid drug reservoir being inoperable communication with the bore of the microneedle at a locationdistal to the tip end of the microneedle. The fluid reservoir may beintegral with the microneedle, integral with the elongated body, orseparate from both the microneedle and elongated body.

Fabrication of the Microneedles

The microneedle can be formed/constructed of different biocompatiblematerials, including metals, glasses, semi-conductor materials,ceramics, or polymers. Examples of suitable metals includepharmaceutical grade stainless steel, gold, titanium, nickel, iron,gold, tin, chromium, copper, and alloys thereof. The polymer can bebiodegradable or non-biodegradable. Examples of suitable biocompatible,biodegradable polymers include polylactides, polyglycolides,polylactide-co-glycolides (PLGA), polyanhydrides, polyorthoesters,polyetheresters, polycaprolactones, polyesteramides, poly(butyric acid),poly(valeric acid), polyurethanes and copolymers and blends thereof.Representative non-biodegradable polymers include various thermoplasticsor other polymeric structural materials known in the fabrication ofMedical devices. Examples include nylons, polyesters, polycarbonates,polyacrylates, polymers of ethylene-vinyl acetates and other acylsubstituted cellulose acetates, non-degradable polyurethanes,polystyrenes, polyvinyl chloride, polyvinyl fluoride, poly(vinylimidazole), chlorosulphonate polyolefins, polyethylene oxide, blends andcopolymers thereof. Biodegradable microneedles can provide an increasedlevel of safety compared to non-biodegradable ones, such that they areessentially harmless even if inadvertently broken off into the oculartissue.

The microneedle can be fabricated by a variety of methods known in theart or as described in the Examples below. In one embodiment, the hollowmicroneedle is fabricated using a laser or similar optical energysource. In one example, a microcannula may be cut using a laser torepresent the desired microneedle length. The laser may also be use toshape single or multiple tip openings. Single or multiple cuts may beperformed on a single microcannula to shape the desired microneedlestructure. In one example, the microcannula may be made of metal such asstainless steel and cut using a laser with a wavelength in the infraredregion of the light spectrum (0.7-300 μm). Further refinement may beperformed using metal electropolishing techniques familiar to those inthe field. In another embodiment, the microneedle length and optionalbevel is formed by a physical grinding process, which for example mayinclude grinding a metal cannula against a moving abrasive surface. Thefabrication process may further include precision grinding, micro-beadjet blasting and ultrasonic cleaning to form the shape of the desiredprecise tip of the microneedle.

Further details of possible manufacturing techniques are described, forexample, in U.S. Patent Application Publication No. 2006/0086689 A1 toRaju et al., U.S. Patent Application Publication No. 2006/0084942 to Kimet al., U.S. Patent Application Publication No. 2005/0209565 to Yuzhakovet al., U.S. Patent Application Publication No. 2002/0082543 A1 to Parket al., U.S. Pat. No. 6,334,856 to Allen et al., U.S. Pat. No. 6,611,707to Prausnitz et al., U.S. Pat. No. 6,743,211 to Prausnitz et al., all ofwhich are incorporated herein by reference for their disclosure ofmicroneedle fabrication techniques.

Fluid Drug Formulation

The fluid drug formulation may be in the form of a liquid drug, a liquidsolution that includes a drug in a suitable solvent, or liquidsuspension. The liquid suspension may include microparticles ornanoparticles dispersed in a suitable liquid vehicle for infusion. Invarious embodiments, the drug may be included in the liquid vehicle, inthe microparticles or nanoparticles, or in both the vehicle andparticles. The fluid drug formulation is sufficiently fluid to flow intoand within the suprachoroidal space. In a preferred embodiment, theviscosity of the fluid drug formulation is about 1 cP at 37° C.

A wide range of drugs may be formulated for delivery to ocular tissueswith the present microneedle devices and methods. As used herein, theterm “drug” refers to essentially any prophylactic, therapeutic, ordiagnostic agent, i.e., an ingredient useful for medical, veterinary, orcosmetic applications. The drug may be selected from suitable proteins,peptides and fragments thereof, which can be naturally occurring,synthesized or recombinantly produced. The drug may be selected fromsuitable oligonucleotides (e.g., antisense oligonucleotide agents),polynucleotides (e.g., therapeutic DNA), ribozymes, dsRNAs, siRNA, RNAi,gene therapy vectors, and/or vaccines for therapeutic use. The drug maybe an aptamer (e.g., an oligonucleotide or peptide molecule that bindsto a specific target molecule).

Representative examples of types of drugs for delivery to ocular tissuesinclude antibiotics, antiviral agents, analgesics, anesthetics,antihistamines, anti-inflammatory agents, and antineoplastic agents.Non-limiting examples of specific drugs and classes of drugs includeβ-adrenoceptor antagonists (e.g., carteolol, cetamolol, betaxolol,levobunolol, metipranolol, timolol), miotics (e.g., pilocarpine,carbachol, physostigmine), sympathomimetics (e.g., adrenaline,dipivefrine), carbonic anhydrase inhibitors (e.g., acetazolamide,dorzolamide), prostaglandins, anti-microbial compounds, includinganti-bacterials and anti-fungals (e.g., chloramphenicol,chlortetracycline, ciprofloxacin, framycetin, fusidic acid, gentamicin,neomycin, norfloxacin, ofloxacin, polymyxin, propamidine, tetracycline,tobramycin, quinolines), anti-viral compounds (e.g., acyclovir,cidofovir, idoxuridine, interferons), aldose reductase inhibitors,anti-inflammatory and/or anti-allergy compounds (e.g., steroidalcompounds such as betamethasone, clobetasone, dexamethasone,fluorometholone, hydrocortisone, prednisolone and non-steroidalcompounds such as antazoline, bromfenac, diclofenac, indomethacin,lodoxamide, saprofen, sodium cromoglycate), artificial tear/dry eyetherapies, local anesthetics (e.g., amethocaine, lignocaine,oxbuprocaine, proxyrnetacaine), cyclosporine, diclofenac, urogastroneand growth factors such as epidermal growth factor, mydriatics andcycloplegics, mitomycin C, and collagenase inhibitors and treatments ofage-related macular degeneration such as pegagtanib sodium, ranibizumab,and bevacizumab.

In certain embodiments the drug may be an integrin antagonist, aselectin antagonist, an adhesion molecule antagonist (e.g.,Intercellular Adhesion Molecule (ICAM)-1, ICAM-2, ICAM-3, PlateletEndothelial Adhesion Molecule (PCAM), Vascular Cell Adhesion Molecule(VCAM)), or a leukocyte adhesion-inducing cytokine or growth factorantagonist (e.g., Tumor Netictosis Factor-α (TNF-α), Interleukin-1β(IL-1β), Monocyte Chemotatic Protein-1 (MCP-1) and a VascularEndothelial Growth Factor (VEGF)), as described in U.S. Pat. No.6,524,581 to Adamis. In certain other embodiments, the drug may besub-immunoglobulin antigen-binding molecules, such as Fv immunoglobulinfragments, minibodies, and the like, as described in U.S. Pat. No.6,773,916 to Thiel et al. In another embodiment, the drug may be adiagnostic agent, such as a contrast agent, known in the art.

The drug typically needs to be formulated for storage and delivery viathe microneedle device described herein. The “drug formulation” is aformulation of a drug, which typically includes one or morepharmaceutically acceptable excipient materials known in the art. Theterm “excipient” refers to any non-active ingredient of the formulationintended to facilitate handling, stability, dispersibility, wettability,release kinetics, and/or injection of the drug. In one embodiment, theexcipient may include or consist of water or saline.

In one embodiment, the fluid drug formulation includes microparticles ornanoparticles, either of which includes at least one drug. Desirably,the microparticles or nanoparticles provide for the controlled releaseof drug into the ocular tissue. As used herein, the term “microparticle”encompasses microspheres, microcapsules, microparticles, and beads,having a number average diameter of 1 to 100 μm, most preferably 1 to 25μm. The term “nanoparticles” are particles having a number averagediameter of 1 to 1000 nm. Microparticles may or may not be spherical inshape. “Microcapsules” are defined as microparticles having an outershell surrounding a core of another material. The core can be liquid,gel, solid, gas, or a combination thereof. In one case, the microcapsulemay be a “microbubble” having an outer shell surrounding a core of gas,wherein the drug is disposed on the surface of the outer shell, in theouter shell itself, or in the core. (Microbubbles may be respond toacoustic vibrations as known in the art for diagnosis or to burst themicrobubble to release its payload at/into a select ocular tissue site.)“Microspheres” can be solid spheres, can be porous and include asponge-like or honeycomb structure formed by pores or voids in a matrixmaterial or shell, or can include multiple discrete voids in a matrixmaterial or shell. The microparticle or nanoparticles may furtherinclude a matrix material. The shell or matrix material may be apolymer, amino acid, saccharide, or other material known in the art ofmicroencapsulation.

The drug-containing microparticles or nanoparticles may be suspended inan aqueous or non-aqueous liquid vehicle. The liquid vehicle may be apharmaceutically acceptable aqueous solution, and optionally may furtherinclude a surfactant. The microparticles or nanoparticles of drugthemselves may include an excipient material, such as a polymer, apolysaccharide, a surfactant, etc., which are known in the art tocontrol the kinetics of drug release from particles.

In one embodiment, the fluid drug formulation further includes an agenteffective to degrade collagen or GAG fibers in the sclera, which mayenhance penetration/release of the drug into the ocular tissues. Thisagent may be, for example, an enzyme, such a hyaluronidase, acollagenase, or a combination thereof. In a variation of this method,the enzyme is administered to the ocular tissue in a separate stepfrom—preceding or following—infusion of the drug. The enzyme and drugare administered at the same site.

In another embodiment, the drug formulation is one which undergoes aphase change upon administration. For instance, a liquid drugformulation may be injected through hollow microneedles into thesuprachoroidal space, where it then gels and the drug diffuses out fromthe gel for controlled release.

Control Features for Directing Movement of the Microneedle in theMethods of Use

The microneedle device may comprise a means for controllably inserting,and optionally retracting, the microneedle into the ocular tissue. Inaddition, the microneedle device may include means of controlling theangle at which the at least one microneedle is inserted into the oculartissue (e.g., by inserting the at least one microneedle into the surfaceof the ocular tissue at an angle of about 90 degrees).

The depth of microneedle insertion into the ocular tissue can becontrolled by the length of the microneedle, as well as other geometricfeatures of the microneedle. For example, a flange or other a suddenchange in microneedle width can be used to limit the depth ofmicroneedle insertion. The microneedle insertion can also be controlledusing a mechanical micropositioning system involving gears or othermechanical components that move the microneedle into the ocular tissue acontrolled distance and, likewise, can be operated, for example, inreverse, to retract the microneedle a controlled distance. The depth ofinsertion can also be controlled by the velocity at which themicroneedle is inserted into the ocular tissue. The retraction distancecan be controlled by elastic recoil of the ocular tissue into which themicroneedle is inserted or by including an elastic element within themicroneedle device that pulls the microneedle back a specified distanceafter the force of insertion is released.

The angle of insertion can be directed by positioning the microneedle ata first angle relative to the microneedle base and positioning the baseat a second angle relative to the ocular surface. In one embodiment, thefirst angle can be about 90° and the second angle can be about 0°. Theangle of insertion can also be directed by having the microneedleprotrude from a device housing through a channel in that housing that isoriented at a specified angle.

One skilled in the art may adapt mechanical systems known in the art incombination with the disclosure set forth herein and in the Examplesbelow to devise suitable structures to controllably drive themicroneedle insertion, which structures may be manually operable,electromechanically operable, or a combination thereof.

Control of Transport Through Microneedle

The transport of drug formulation or biological fluid through a hollowmicroneedle can be controlled or monitored using, for example, one ormore valves, pumps, sensors, actuators, and microprocessors. Forinstance, in one embodiment the microneedle device may include amicropump, microvalve, and positioner, with a microprocessor programmedto control a pump or valve to control the rate of delivery of a drugformulation through the microneedle and into the ocular tissue. The flowthrough a microneedle may be driven by diffusion, capillary action, amechanical pump, electroosmosis, electrophoresis, convection or otherdriving forces. Devices and microneedle designs can be tailored usingknown pumps and other devices to utilize these drivers. In oneembodiment, the microneedle device may further include an iontophoreticapparatus, similar to that described in U.S. Pat. No. 6,319,240 to Beck,for enhancing the delivery of the drug formulation to the ocular tissue.In another embodiment the microneedle devices can further include aflowmeter or other means to monitor flow through the microneedles and tocoordinate use of the pumps and valves.

The flow of drug formulation or biological fluid can be regulated usingvarious valves or gates known in the art. The valve may be one which canbe selectively and repeatedly opened and closed, or it may be asingle-use type, such as a fracturable barrier. Other valves or gatesused in the microneedle devices can be activated thermally,electrochemically, mechanically, or magnetically to selectivelyinitiate, modulate, or stop the flow of material through themicroneedles. In one embodiment, the flow is controlled with arate-limiting membrane acting as the valve.

The present invention may be further understood with reference to thefollowing non-limiting examples.

EXAMPLES

Experiments were conducted to evaluate whether microneedles could beused to pierce to the base of the sclera and target the suprachoroidalspace. More specifically, experiments were conducted to evaluate whetherhollow microneedles can deliver small molecules and particles to thesuprachoroidal space of pig, rabbit and human cadaver eyes. Additionalexperiments were conducted to measure the effect of microneedle length,infusion pressure, and intraocular pressure on the delivery of particlesranging from 20-1000 nm in diameter in pig eyes. Finally, experimentswere conducted to examine the role that particle size plays and theinfluence of ocular anatomical barriers on delivery to thesuprachoroidal space.

Whole rabbit eyes (Pel-Freez Biologicals, Rogers, Ark.), pig eyes(Sioux-Preme Packing, Sioux Center, Iowa) and human eyes (Georgia EyeBank, Atlanta, Ga.), all with the optic nerve attached, were shipped onice and stored wet at 4° C. for up to 3 days. Prior to use, eyes wereallowed to come to room temperature and any fat and conjunctiva wereremoved to expose the sclera.

Hollow microneedles were fabricated from borosilicate micropipette tubes(Sutter Instrument, Novato, Calif.), as described previously (J. Jiang,et al., Pharm. Res. 26:395-403 (2009)). FIG. 7A shows a comparison ofthe hollow microneedle compared to the tip of a 30 gauge hypodermicneedle (scale=500 μm). A custom, pen-like device with a threaded cap wasfabricated to position the microneedle and allow precise adjustment ofits length. This device was attached to a micropipette holder (MMP-KIT,World Precision Instruments, Sarasota, Fla.) with tubing that wasconnected to a carbon dioxide gas cylinder for application of infusionpressure. The holder was attached to a micromanipulator (KITE, WorldPrecision Instruments) which was used to control insertion of themicroneedle into the sclera.

Carboxylate-modified FluoSpheres® (Invitrogen, Carlsbad, Calif.) wereinjected as 2 wt % solids suspension of 20 nm, 100 nm, 500 nm, and 1000nm diameter particles. Tween 80 (Sigma-Aldrich, St. Louis, Mo.) at afinal concentration of 0.5 wt %, was added to the suspension andsonicated prior to use. Sulforhodamine B (Sigma-Aldrich) was dissolvedin Hanks' balanced salt solution (Mediatech, Manassas, Va.) to make asulforhodamine solution of 10⁻⁴ M. Barium sulfate particles (FisherScientific, Waltham, Mass.) measuring 1 μm in diameter were suspended inbalanced salt solution (BSS Plus, Alcon, Fort Worth, Tex.) to form a 1.5wt % suspension.

A custom acrylic mold, shaped to fit a whole eye, was built to hold theeye steady and used for all experiments (FIG. 7B). A catheter wasinserted through the optic nerve into the vitreous and connected to abottle of BSS Plus raised to a height to generate internal eye pressure(18 or 36 mm Hg). Suction was applied to a channel within the mold tohold the external surface of the eye steady during microneedle insertionand manipulation. Each microneedle was pre-filled with a desired volumeof the material to be injected. The microneedle was placed in the deviceholder at a set microneedle length, attached to the micromanipulator andconnected to the constant pressure source. Microneedles were theninserted perpendicular to the sclera tissue 5-7 mm posterior from thelimbus. A set pressure was applied to induce infusion. Thirty secondswere allowed to see if infusion of the solution began. If infusionoccurred, the pressure was stopped immediately upon injection of thespecified volume. If visual observation of the injected material showedlocalization in the suprachoroidal space, the injection was considered asuccess. If infusion had not begun within that timeframe, then theapplied pressure was stopped and the needle was retracted. This wasconsidered an unsuccessful delivery.

Eyes to be imaged using microscopy were detached from the set-up withinminutes after delivery was completed. The eyes were placed in acetone orisopentane kept on dry ice or liquid nitrogen, causing the eye to freezecompletely within minutes after placement. The frozen eye was removedfrom the liquid and portions of the eye were hand cut using a razorblade for imaging of injected material. Imaging was performed using astereo microscope using brightfield and fluorescence optics (model SZX12, Olympus America, Center Valley, Pa.). The portions containing thesclera, choroid and retina were placed in Optimal Cutting Temperaturemedia (Sakura Finetek, Torrance, Calif.) and frozen under dry ice orliquid nitrogen. These samples were cryosectioned 10-30 μm thick (MicromCryo-Star HM 560MV, Walldorf, Germany) and imaged by brightfield andfluorescence microscopy (Nikon E600, Melville, N.Y.) to determine thelocation of injected material in the eye. Images were collaged asnecessary using Adobe Photoshop software (Adobe Systems, San Jose,Calif.).

Pig eyes used for microcomputed tomography imaging were not frozen afterinjection. Instead, pig eyes were injected with a barium sulfatesuspension and stabilized in a 30 mm diameter sample tube and scanned inair using a Scanco μCT40 desktop conebeam system (Scam) Medical AG,Briittisellen, Switzerland) at 30 μm isotropic voxel size, E=55 kVp,I=145 μA, and integration time=200 ms. Through a convolutionbackprojection algorithm based on techniques from Feldkamp et. al. (J.Opt. Soc. AM. A-Opt. Image Sci. Vis. 1:612-619 (1984)), raw data wereautomatically reconstructed to generate 2D grayscale tomograms. Globalsegmentation values (Gauss sigma, Gauss support, and threshold) werechosen for the contrast-enhanced region as well as general eye tissue.Grayscale tomograms were stacked, and 3D binarized images were producedby applying the optimal segmentation values (one image for the entireeye and another for the region injected with contrast agent). Theseimages were overlayed using Scanco image processing language todemonstrate the relative 3D position of the contrast-enhanced regionwithin the entire eye.

Example 1 Delivery of a Model Compound to the Suprachoroidal Space Usinga Hollow Microneedle

Red-fluorescent sulforhodamine B was used as a model compound andinjected into pig eyes ex vivo using a single hollow microneedleinserted just to the base of the sclera in order to target thesuprachoroidal space. A brightfield microscopic image of the saggitalcross section of an untreated pig eye, shown in FIGS. 8A and 8B (Scalebar: 500 μm), was taken both before and after injection of 35 μL ofsulforhodamine B. The normal ocular tissue (FIG. 8A) can bedistinguished to identify the sclera, choroid, retina, and vitreoushumor. After infusion of the model compound (FIG. 8B), thesulforhodamine solution can be seen just below the sclera and above thechoroid in the suprachoroidal space, confirming that the solution wasinjected and spread within the suprachoroidal space from the initialinjection site. Volumes up to 35 μL were able to be injected withoutleakage, but larger volumes leaked out from openings on the surface ofthe eye where vortex veins would be attached in vivo. However,subsequent experiments in pigs and rabbits in vivo have demonstratedsuprachoroidal delivery of up to 100 μL without leakage through theseopenings (data not shown).

Example 2 Delivery of Particles to the Suprachoroidal Space Using HollowMicroneedles

Particles with diameters of 500 nm or 1000 nm were injected into thesuprachoroidal space of rabbit, pig and human eyes ex vivo and imaged toevaluate the distribution and localization of the particles just belowthe sclera. The sclera (1), choroid (2), and retina (3) were identifiedin a fluoroscopic image of a cryosection of a pig eye with no infusioninto the suprachoroidal space (FIG. 9A, Scale bar: 500 μm). Fluoroscopicimages of cryosections of a rabbit eye after injection of 500 nmparticles were taken in the axial plane and the images were collaged toform a panoramic view (FIG. 9B, Scale bar: 500 μm). The spread of thefluorescent particles (which appear as the bright white regions in theimages) was observed along the equator of the eye in a thin sheath justbelow the sclera. A volume of 15 μL was injected and, in this particularcross-section taken in the plane of the insertion site, the injectionhad spread approximately 20 mm, which corresponds to about 36% of thetotal circumference of the eye.

Fluoroscopic images of cryosections of pig and human eyes were taken inthe sagittal directions so that the images show the anterior of the eyeto the right and the posterior of the eye to the left (FIGS. 9C and 9D,respectively). These images show the ability of microinjected particles(which appear bright white) to spread in the suprachoroidal space bothin the anterior and posterior direction of the eye from the injectionsite. In these experiments, a single microneedle delivered 30 μL of a 2wt % particle suspension into the suprachoroidal space of both species.Leakage was observed at the vortex vein openings away from the injectionsite similar to what was observed with sulforhodamine injections.

The insets in these images show magnified views of the microneedleinsertion site. In each case, the insertion site within the sclera wasfilled with particles. In the case of the pig (FIG. 9C) and human (FIG.9D), the retina was still attached and visible, and it was clear thatthe microneedle had not penetrated to the retina. In the case of therabbit (FIG. 9B), the retina separated during the cryosectioningprocedure and was not visible. These results confirmed that amicroneedle was able to target the suprachoroidal space of rabbit, pig,and human eyes to deliver particles up to 1000 nm in diameter. Theresults further confirmed that these particles spread from the injectionsite circumferentially in all directions within the suprachoroidalspace.

Microcomputed tomography (μCT) was utilized to image the circumferentialspread and localization of injected material in the suprachoroidal spacein three dimensions using a noninvasive method. After injecting 35 μL of1 μm diameter barium sulfate contrast agent particles into thesuprachoroidal space of a pig eye, cross sectional images showed theparticles distributed as a thin white strip that circled just below theouter edge of the eye, i.e., just below the sclera (FIG. 10A). Thisprofile is characteristic of suprachoroidal delivery and similar to theresults from fluorescence imaging. The three-dimensional reconstructionof these cross-sectional images showed the spread of the particles inthe posterior segment of the eye (FIG. 10B, Scale Bar: 5 mm). Theparticles spread was approximately 5 mm in radius, althoughasymmetrically distributed around the injection site, and covered anapproximate area of 70 mm² (which represents 7% of the surface area ofthe back of the eye). This further confirmed the ability of microneedlesto spread particles over a significant portion of the posterior segmentof the eye by targeting the suprachoroidal space.

Example 3 Effect of Operating Parameters on Particle Delivery to theSupradioroidal Space

Particles of 20, 100, 500, and 1000 nm diameter were injected into pigeyes ex vivo using a range of different microneedle lengths and infusionpressures to determine the success rate of suprachoroidal delivery. Anattempted injection was considered to be either fully successful(complete injection of the 25 μL particle suspension into thesuprachoroidal space) or fully unsuccessful (an inability to inject atall). No partial injections were observed. The effect of infusionpressure and microneedle length on the success rate of suprachoroidaldelivery of particles are shown for 20 nm (FIG. 11A), 100 nm (FIG. 11B),500 nm (FIG. 11C), and 1000 nm (FIG. 11D) particles into pig eyes.

The success rate increased with greater infusion pressure and withgreater microneedle length (ANOVA, p<0.05). For the 20 nm particles(FIG. 11A), 100% successful injections were achieved using a pressure of250 kPa at all microneedle lengths. For 100 nm particles (FIG. 11B), theeffects of pressure similarly plateaued at 250 kPa and 100% success wasachieved at all but the shortest microneedle length (700 μm). For thelarger particles (500 and 1000 nm) (FIGS. 11C and 11D, respectively),the effects of pressure generally plateaued at 300 kPa and success ratesignificantly decreased for shorter microneedles. Not wishing to bebound by any theory, it is believed that short microneedles lengthsinject within the sclera, such that particles must be forced through aportion of the sclera to reach the suprachoroidal space. Smallerparticles (20 and 100 nm) can more easily force through a portion of thesclera to reach the suprachoroidal space because the spacing of collagenfiber bundles in the sclera is on the order of 300 nm. Larger particles(500 and 1000 nm), however, have more difficulty crossing this:anatomical barrier, such that infusion pressure becomes a moreimportant parameter and injection success rate decreases significantly.

A statistical comparison of the injection rates of particles ofdifferent sizes at different microneedle lengths was made using ANOVAand is summarized in the following table.

Microneedle 20 vs 100 vs 500 vs 20 vs Length 100 nm 500 nm 1000 nm 1000nm 700 μm 0.02* 0.02* 0.09 0.02* 800 μm 0.37 0.00* 0.10 0.01* 900 μm0.18 0.03* 0.18 0.03* 1000 μm  0.18 0.37 0.21 0.18 Significance wasconsidered to be a p < 0.05 and indicated by an asterisk (*).The statistical analysis showed that at a microneedle length of 700 μm,where the most scleral tissue must be traversed to reach thesuprachoroidal space, success rate depended strongly on particle size.Using 800 and 900 μm microneedles, particles smaller than the collagenfiber spacing (20 and 100 nm) behaved similarly and particles largerthan the collagen fiber spacing (500 and 1000 nm) also behavedsimilarly, but there was a significant difference between 100 nm and 500nm particles. The longest microneedles (1000 μm), which probably reachedthe base of the sclera, showed no significant dependence on particlesize, suggesting that overcoming the collagen barrier in the sclera wasno longer needed.

Not wishing to be bound by any particular theory, the foregoing furthersuggested that particles of 20 and 100 nm can spread within the scleraas well as the suprachoroidal space, whereas particles of 500 and 1000nm should localize exclusively in the suprachoroidal space. The spreadof 20 nm particles (FIG. 12A) was compared to the spread of 1000 nmparticles (FIG. 12B) under identical conditions. As expected, thesmaller particles exhibited significant spread in the sclera as well asthe suprachoroidal space. In contrast, the larger particles wererelegated primarily to the suprachoroidal space and were largelyexcluded from the sclera. This localization of large particles wasconsistent with the results shown in FIG. 11.

Thus, 20 and 100 nm particles were reliably injected using a minimummicroneedle length of 800 μm and a minimum pressure of 250 kPa. Todeliver 500 and 1000 nm particles, a minimum microneedle length of 1000μm and a minimum pressure of 250-300 kPa was required.

Example 4 Effect of Intraocular Pressure on Delivery of Particles to theSuprachoroidal Space

Intraocular Pressure (IOP) is the internal pressure within the eye thatkeeps the eye inflated. It provides a back pressure that can counteractthe infusion pressure. To evaluate the effect of intraocular pressure onparticle delivery to the suprachoroidal space, 1000 nm particles wereinjected at two different levels of IOP, 18 and 36 mmHg. The effect ofinfusion pressure and microneedle length on the success rate ofsuprachoroidal delivery of 1000 nm particles at simulated IOP levels of18 mmHg and 36 mmHg is shown in FIG. 13A and FIG. 13B, respectively. Thedelivery success rate generally increased with an increase in IOP.Notably, at normal IOP, no particles were delivered at the lowestinfusion pressure (150 kPa) or using the shortest microneedles (700 μm)and only the longest microneedles (1000 μm) achieved 100% success rateat the highest infusion pressure (300 kPa) (FIG. 13A). In contrast, atelevated IOP, particles were sometimes delivered at the lowest infusionpressure and using the shortest microneedles, and a 100% success ratewas achieved using both 900 and 1000 μm microneedles at the highestinfusion pressure (FIG. 13B).

Not wishing to be bound by any theory, it is believed that the maineffect of elevated IOP is to make the sclera surface more firm, reducingtissue surface deflection during microneedle insertion and therebyincreasing the depth of penetration into sclera for a microneedle of agiven length. Although we did not measure microneedle insertion depthdirectly, these results suggest that microneedle insertion maybe moreeffective at elevated IOP because they insert deeper into the sclera andthereby increase infusion success rate.

Example 5 Delivery of Model Compound to Suprachoroidal Space in LiveAnimal Models

The delivery of a fluorescent molecule (sodium fluorescein) to thesuprachoroidal space was evaluated using rabbits according to approvedlive animal experimental protocols. A one dimensional scan of the eye(through line of sight) was taken within the first five minutes afterinjection to determine the dispersion of the fluorescent molecule in theeye (FIG. 14). The y-axis indicates the fluorescent intensity (i.e., theconcentration) and the x-axis represents the position in the eye fromfront (160) to back (0). Thus, the results illustrate that within thefirst 5 minutes after injection, the fluorescein had already flowedthrough the suprachoroidal space to the back of the eye, with someremaining at the initial insertion site.

Similar scans were taken to evaluate the rate of clearance offluorescein from the suprachoroidal space over time (FIG. 15). Thefluorescent intensity was measured in two regions of the eye (thesuprachoroidal space and mid-vitreous region) over time. The resultsillustrate that the bulk of the material injected remains in thesuprachoroidal space without passing into the mid-vitreous region andthat the material substantially cleared the suprachoroidal space within24 hours.

Example 6 Delivery of Particles to Suprachoroidal Space in Live AnimalModels

Live animal experiments also were conducted to evaluate the delivery ofparticles to the suprachoroidal space. Fluorescent particles having adiameter of 20 nm and 500 nm were infused into rabbit eyes and thefluorescent intensity was evaluated to determine the length of time theparticles remained in two regions of the eye (the suprachoroidal spaceand mid-vitreous region).

The smaller particles (FIG. 16) were successfully delivered to thesuprachoroidal space and remained in the suprachoroidal space for atleast 35 days. The larger particles (FIG. 17) also were successfullydelivered to the suprachoroidal space and remained in the suprachoroidalspace for at least 24 days. Notably, both the smaller and largerparticles were well localized as indicated by the low level offluorescence in the mid-vitreous region.

Publications cited herein and the materials for which they are cited arespecifically incorporated by reference. Modifications and variations ofthe methods and devices described herein will be obvious to thoseskilled in the art from the foregoing detailed description. Suchmodifications and variations are intended to come within the scope ofthe appended claims.

1. An apparatus for delivery of a drug to the eye comprising: at leastone solid microneedle; a structure or system for controlling insertionof the at least one solid microneedle into the sclera or corneal stromawithout penetrating across the sclera or corneal stroma; and a drugformulation which comprises a drug, wherein the apparatus is adapted todeposit the drug formulation into the sclera or corneal stroma to form adrug depot for controlled release of the drug to an ocular tissue. 2.The apparatus of claim 1, wherein the structure for controllinginsertion comprises a flange configured to limit the depth of insertionof the at least one solid microneedle into the sclera or corneal stroma.3. The apparatus of claim 1, wherein the system for controllinginsertion comprises a mechanical micropositioning system to move the atleast one solid microneedle and to limit the depth of insertion of theat least one solid microneedle into the sclera or corneal stroma.
 4. Theapparatus of claim 1, wherein the apparatus comprises a housing having achannel from which the at least one solid microneedle can be operablyextended at a specified angle for insertion into the sclera or cornealstroma.
 5. The apparatus of claim 1, wherein the drug formulation is inthe form of a coating on the at least one microneedle.
 6. The apparatusof claim 5, wherein the coating is configured to dissolve or detach fromthe at least one microneedle upon insertion into the sclera or cornealstroma.
 7. The apparatus of claim 1, wherein the drug formulationcomprises microparticles or nanoparticles, the microparticles ornanoparticles comprising the drug.
 8. The apparatus of claim 1, whereinthe drug is an anti-inflammatory drug.
 9. The apparatus of claim 1,wherein the at least one microneedle extends from the base an angle ofabout 90 degrees.
 10. The apparatus of claim 1, further comprising animaged-guided feedback system operable to determine the location of themicroneedle in the eye.
 11. The apparatus of claim 1, wherein the atleast one microneedle has an effective length between 500 microns and1000 microns.
 12. The apparatus of claim 1, wherein the at least onemicroneedle has a maximum cross-sectional width or diameter of 400microns.
 13. The apparatus of claim 1, wherein the at least onemicroneedle is formed of metal and comprises a cylindrical shaft havingan outer diameter of between 200 microns and 400 microns, and a beveledtip less than about 400 microns in length.
 14. A method of administeringa drug to an eye of a patient, comprising: inserting a solid microneedleinto the sclera or corneal stroma of the eye at an insertion sitewithout the microneedle penetrating across the sclera or corneal stroma,the solid microneedle comprising a drug formulation which comprises adrug; and forming a drug depot at the insertion site in the sclera orcomeal stroma for controlled release of the drug to an ocular tissue.15. The method of claim 14, wherein the drug formulation is in the formof a coating on the solid microneedle.
 16. The method of claim 15,wherein the coating dissolves or detaches from the at least onemicroneedle upon insertion into the sclera or corneal stroma.
 17. Themethod of claim 14, wherein the drug depot comprises microparticles ornanoparticles, the microparticles or nanoparticles comprising the drug.18. The method of claim 14, wherein the drug is an anti-inflammatorydrug.
 19. The method of claim 14, wherein the insertion site is at aboutthe equator of the eye or between the equator and the limbus of the eye.